Three-dimensional scanning transmission electron microscopy of dislocation loops in tungsten.

Scanning transmission electron microscopy (STEM) imaging using diffraction contrast is a powerful technique to assess crystal defects. In this work it is used to assess the spatial distribution of radiation induced defect in tungsten. In effect, its irradiation leads to the formation of nanometric dislocation loops that under certain conditions may form intriguing 3-D rafts. In this study, we have irradiated thin tungsten samples in situ in a TEM with 1.2 MeV W ions to 0.017 dpa at room temperature (RT) and at 700 °C. Besides the Burgers vector analysis, the number density and size of the dislocation loops with their spatial arrangement were quantitatively characterized by stereo imaging in STEM mode. Most of the loops have a Burgers vector ½ a0 〈111〉, with some a0 〈100〉 at room temperature. Loops are located mainly in the simulated damage profile but there is also a significant portion in deeper regions of the sample, indicating that loops in W diffuse easily, even at RT. At 700 °C, loops form elongated rafts that contain dislocation segments having a Burgers vector ½ a0 〈111〉. The rafts are narrow and reside on {111} planes; they are elongated along 〈110〉 directions, which correspond, when combined to the rafts' Burgers vector, to the lines of edge dislocations. Compared to conventional TEM, 3-D analysis in STEM appears thus as a powerful technique for quantitative analyses of defects in tungsten, as it allows reducing the background diffraction contrast and reaching thicker areas of the electron transparent foil, here 0.5 µm of tungsten at 200 kV.

Auditory electrical tinnitus suppression in patients with and without implants.

The aim of this study was to evaluate the effectiveness of electrical tinnitus suppression in two groups of chronic severe tinnitus sufferers. Through standard tinnitus questionnaires, we compared the effectiveness of extratympanic and intratympanic auditory electrical stimulation (AES) by cochlear implants (CI) for the suppression or abolition of the perception of tinnitus and the decrease of its associated complaints. We made otolaryngological and comprehensive audiological assessment and also tinnitus measurement in each group of patients before and after AES and 50 days later. We investigated the dimensions of psychological complaints due to chronic and disabling tinnitus by means of the tinnitus questionnaire (TQ). The control examination during at least seven sessions (50 days) after AES in the group of patients without implants showed improvement in 20 of 32 patients (62.5%); 12 (37.5%) did not notice any change. In the comparative group of patients with implants, improvement occurred in 16 of 20 patients (75%); during the switch-on of the speech processor, these patients reported significant attenuation or complete suppression of their tinnitus. Complete suppression of the tinnitus after CI was observed for 11 patients (55%), and 5 patients (25%) demonstrated significant attenuation of tinnitus. Nonsuppression of tinnitus was observed for only 4 patients (25%). None of our patients was affected by an increment in the tinnitus owing to CI. The differences of means of scores in the standard TQ were significant in both groups of patients. A comparison of TQ score differences between patients with and without implants showed no significance. We concluded that AES is a useful and effective therapeutic intervention in patients with tinnitus. Extratympanic AES reduces the effects of the tinnitus but presents limitations, mainly owing to the short duration of the electrical residual inhibition of the tinnitus. CI is shown to be more efficient for the treatment of tinnitus, mainly because the electrical stimulation affects a wider area of the cochlea and is presented for longer sessions. Therefore, patients affected by incapacitating tinnitus should be considered for continuous use of electrical stimulation.